(1) Technical Field
This invention relates to a method which varies the amount of pressure applied to specific areas of a semiconductor during polishing and permits more accurate control of the polishing rate across the semiconductor surface when performing chemical mechanical polishing (CMP) to produce a uniform substrate surface.
(2) Description of the Prior Art
The following documents relate to a method for controlling a polishing rate across a substrate surface when performing CMP.
U.S. Pat. No. 5,423,716 issued Jan. 5, 1994 to Alan Strasbaugh describes an apparatus for holding a wafer which includes a soft, resilient membrane that covers a horizontal backing plate. The lower face of the backing plate includes a number of recessed areas to which vacuum can be selectively applied. By applying a pressurized fluid to the recessed areas during polishing, the membrane will exert a uniform downward pressure on the wafer and produce a uniformly polished surface.
U.S. Pat. No. 5,624,299 issued May 1, 1995 to Norman Shendon describes a carrier apparatus for positioning and biasing a substrate against a polishing pad. The device uses a membrane configured to create one or more vacuum regions which chuck the substrate to the membrane so that the carrier may move the substrate on and off the polishing pad.
U.S. Pat. No. 5,800,248 issued Apr. 26, 1996 to Anil K. Pant et al describes a support housing which underlies a polishing pad and includes a plurality of openings for dispensing a pressurized fluid.
The manufacture of an integrated circuit device requires the formation of various layers (both conductive and non-conductive) above a substrate to form the necessary components and interconnects. During the manufacturing process, certain layers or portions of layers must be removed in order to pattern and form the various components and interconnects. Chemical mechanical polishing (CMP) is the method of choice for planarization of a surface of a semiconductor wafer, such as a silicon wafer, at various stages of the integrated circuit processing. CMP is also used to flatten optical surfaces, metrology samples and in various metal and semiconductor based substrates.
CMP is a technique in which a chemical slurry is used in conjunction with a mechanical polishing pad to polish away materials on a semiconductor wafer. The mechanical movement of the pad relative to the wafer (and in conjunction with the slurry) provides the abrasive force to polish the exposed surface of the wafer. In the most common form of CMP, a substrate is mounted on a polishing head which rotates against a polishing pad placed on a rotating table. The mechanical force derives from the rotating table speed and the downward pressure on the head. The chemical slurry is constantly transferred under the polishing head. Rotation of the polishing head helps in the slurry delivery as well as in averaging the polishing rates across the substrate surface. A constant problem of CMP is that the polishing rate varies from the periphery to the center of the wafer for various reasons. Pad bounce is one reason. Variations in the velocity encountered in the rotational movement is another. Some amount of averaging is achieved by rotating the wafer but variations still result in non-uniform polishing across the wafer surface. It is an important goal in the CMP processing to try to minimize this inequality in polishing rates.
One approach utilizes a linear polisher as opposed to a rotating one. A moving belt linearly moves the pad across the wafer surface. The wafer is still rotated for averaging out the local variations, but the global planarity is improved over CMP tools using rotating pad.